#7102 Fix enhanced client list projection placeholders

[arnabnandy7]

Motivation and Context

Fixes #7102.

addAttributeToProject("tags[0]") in the DynamoDB Enhanced Client generated an invalid ExpressionAttributeNames key containing brackets, such as #AMZN_MAPPED_tags[0]. DynamoDB rejects that key. The placeholder should map only the attribute name, while the list dereference remains in the projection expression.

Modifications

• Updated ProjectionExpression to strip trailing list dereferences when generating expression attribute name placeholders.
• Preserved list dereference suffixes in the final projection expression, so tags[0] now produces:
  • ExpressionAttributeNames: { "#AMZN_MAPPED_tags": "tags" }
  • ProjectionExpression: "#AMZN_MAPPED_tags[0]"
• Added unit coverage for projection expressions with list dereferences, including nested paths.
• Added scan request generation coverage for ScanEnhancedRequest.builder().addAttributeToProject("tags[0]").
• Added a changelog entry via scripts/new-change.

Testing

• Ran git diff --check successfully.
• Attempted targeted Maven test runs, but local verification was blocked by unrelated repository/build state:
  • module-only test run could not resolve local snapshot artifacts: dynamodb and service-test-utils
  • reactor -am run hit unrelated generated-region clobber/stale target output and Apache client target-class issues before reaching the enhanced client tests

Screenshots (if appropriate)

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have read the CONTRIBUTING document
• Local run of mvn install succeeds
• My code follows the code style of this project
• My change requires a change to the Javadoc documentation
• I have updated the Javadoc documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed
• I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.
• My change is to implement 1.11 parity feature and I have updated LaunchChangelog

License

• I confirm that this pull request can be released under the Apache 2 license